Research On 780 Nm Fiber Laser Based On PPLN Crystal Frequency Doubling Technology

Atomic interference technology utilizes the wave-particle duality(material wave)of an atom to achieve high-precision measurement techniques by laser manipulation of atomic interference.The control laser required by the atomic interferometer platform supported by this paper is 780 nm,which requires good beam quality,no jitter,stable frequency and long-term frequency drift,and the working state is not easily affected by the environment.In this paper,a distributed feedback(DFB)laser is used to generate a 1560 nm laser and a phase-polarized Lithium Niobate(PPLN)crystal is doubling to 780 nm.The laser system is developed.The content is as follows:1)Explain the basic principles of laser generation.Lasers need to meet three conditions at the same time: particle number inversion,optical cavity and gain medium.Among them,the particle beam inversion means that the atoms in the high energy level are more than the low level atoms;the optical resonator can reflect the laser multiple times;the gain medium can increase the laser power.2)Theoretical study of 780 nm fiber laser based on PPLN crystal frequency doubling technology.The process of multiplying the fundamental light of frequency ω can be divided into two steps: first,a polarized wave having a frequency of 2ω is generated.In the second step,the energy is converted from polarized waves to a frequency of 2ω.In order to achieve effective conversion between the two,the frequency doubled light and the frequency doubled light need to meet certain quasi-phase matching conditions.3)Set up a test system with a 1560 nm laser frequency doubling to 780 nm.The distributed feedback laser is used as a seed source to generate 20 mW of 1560 nm seed light,which is amplified to 8 W by an Erbium-doped Fiber Amplifier(EDFA),and focused into a PPLN frequency doubling crystal for quasi-phase matching.Finally,a 1.2 W 780 nm laser was obtained.4)Design PPLN crystal temperature control system.The PPLN crystal is held by brass with excellent thermal conductivity.The temperature information is collected by the thermistor and fed back to the PID controller.The controller compares the collected information with the set value,adjusts the input current of the thermoelectric cooler,and then changes the temperature of the PPLN crystal to realize a closed loop control loop.The system temperature control range is-14.7 ° C~105.0 ° C,temperature control accuracy is ± 0.005 ° C.5)In order to verify that the obtained 780 nm frequency doubled laser has a certain wavelength tunable range,a saturated absorption optical path of germanium atoms is constructed to obtain a saturated absorption spectrum,which proves that the wavelength and power of the obtained frequency doubled laser meet the requirements of the cold atom interferometer system.6)The designed laser is stabilized by Modulation Transfer Spectroscopy(MTS).Compared with the passive measures such as vibration isolation and temperature control for the laser,the feedback control system of the active frequency stabilization technology can actively cancel the variation of the laser frequency,thereby achieving the purpose of narrowing the laser line width.